Transistor ignition circuits with a control transformer



April 13, 1965 J. M KENDRY 3,178,608

TRANSISTOR IGNITION CIRCUITS WITH A CONTROL TRANSFORMER Filed May 16, 1961 3 Sheets-Sheet 1 I l 17 M o nun 20 mmvrox FRANCLS JMQYZNDRY ATTORNEY April 13, 1965 F. J. M KENDRY 3,178,608

TRANSISTOR IGNITION CIRCUITS WITH A CONTROL TRANSFORMER Filed May 16, 1961 3 Sheets-Sheet 2 G; a v29: 4 60MMONW1TIR COMMON COLLECTOR IN V EN TOR. pAnastzMsnNmy April 13, 1965 F. J. MCKENDRY 3 Sheets-Sheet 5 Filed May 16, 1961 NwNNN NEIGNW POINT 6' OPEN INVENTOR. {$45 615 J. MHQWAQY ATIUPNIY United States Patent Office P 3,178,608 atented Apr. 13, 1965 3,178,608 TRANSISTOR IGNITION CIRCUITS WITH A CONTROL TRANSFORMER Francis John McKendry, Elheron, N.J., assignor to The Bendix Corporation, Eatontown, N.J., a corporation of Delaware Filed May 16, 1961, Ser. No. 110,379 6 Claims. (Cl. 315206) The present invention relates to electrical circuits and more particularly to electrical circuits adapted for use in ignition circuits.

Ignition circuits operate on the principle of stored inductive energy transfer. In the circuit presently employed in most ignition systems, the points or switch, located in the distributor, when closed allows current to flow in the primary winding of the ignition coil. The energy stored in the primary winding is determined by the current flowing through it. Upon the switch or points being opened, in synchronism with mechanical events of the engine to which it is coupled, the electrical inertia of the primary winding to a change in current causes a large voltage buildup across the primary winding. This voltage is coupled by transformer action to the high voltage or secondary winding. Systems using the above methods are objectionable in that the breaker points are subject to excessive wear as they are required tive load. Further such a system has poor starting properties as the voltage introduced in the high voltage or secondary winding varies with the rate at which the current 'is interrupted by the action of the points which move the slowest at cranking speeds. Also a non-uniform high voltage is fed into varying loads, such as from clean to dirty spark plugs.

The present invention provides a circuit in which a transistor controls the current flowing in the primary winding. The switch or points are required only to turn the transistor on or oli, thus the Wear on the points is greatly reduced as they now see an essentially resistive load that is only a small part of the load tormerly handled. Further the transistorized systems provide high energy impulses, even at cranking speeds, as the transistor switches otf rapidly regardless of breaker speed.

- It is an object of the invention to provide an improved electrical circuit.

Another object of the invention is to provide an improved ignition system.

Another object of the invention is to provide an electrical circuit having a fast response.

Another object of the invention is to provide a novel high voltage circuit.

Another object of the invention is to provide an improved ignition system for an internal combustion engme.

Another object of the invention is to provide an ignition system that reduces the wear on the contacts.

The above and other objects and features of the invention will appear more fully hereinafter from a consideration of the following description taken in connection with the accompanying drawings wherein several embodiments are illustrated by way of example.

In the drawing:

FIGURE 1 is a schematic diagram of a transistorized ignition system.

FIGURE 2 is a schematic diagram of a preferred embodiment of an ignition system.

FIGURES 3 and 4 are schematic diagrams of various modifications of the circuit of FIGURE 2.

FIGURE 5 is a curve explaining the operation of the circuit of FIGURE 2.

Referring now to the drawing wherein similar parts in the various figures have been assigned the same reference numbers, in FIGURE 1 an ignition system is indicated generally by the numeral and is of a type adapted for use in motor vehicles. A source of power, tor purposes of illustration, is indicated as a battery 11 and has one terminal connected by a conductor 12 to ground. The other terminal of the battery '11 is connected by conductor 13 to one side of a switch 14. The other side of the switch 14 is connected by conductor 15 to one side of a winding 16 of a transformer '17. Resistors 18 and 19 may be inserted in the conductor '15 The other side of the winding 16 is connected by a conductor 20 to emitter 21 of a transistor 22. In addition to the emitter 21, the transistor 22 has a collector 23 and base 24 and may be -a PNP or NPN of suflicient size to handle the current. The device may have a fast inherent turn off time such as Bendix 2N1073 series or 2Nl650 series. The collector 23 is connected by a conductor 25 to ground. The base 24 of the transistor 22 is connected by conductor 26 to a contact 27 of switch 28. The switch 28 may be the points or breakerof an internal combustion engine and in addition to the contact 27 has a mating contact 29 which is connected by conductor 30 to ground. A zener diode 31 may be con nected across the transistor 22 as a shunt for high voltages.

The trans-former 17 also has a winding 32, one end of which is connected by conductor '33 to ground. The other end of the winding 3-2 is connected by conductor 34 to center terminal 35 of a rotary switch or distributor 36. The distributor '36 has a movable contact 37 adapted for engaging contacts 38, 38N. The contact 37 is mechanically connected to be driven by the engine (not shown). Also driven by the engine in proper sequence with the distributor 36 is a cam 39 for actuating the points 28. The contacts 38, 38N are connected by conductors 40, 40N to spark plugs 41, 41N. The other side of the spark plugs are connected to ground. While only one plug has been illustrated it is understood that it is not limited thereto but may be a plurality.

In addition to the windings 16 and 32, the transformer 17 has a feed-back winding 42, one side of which is connected by conductor 43 to the emitter 21 of the transistor 22. The other side of the winding 42 is connected by conductor 44 and resistor 45 to the base 24 of the transistor 22.

In. operation the aforenoted system has the advantage over the present ignition systems in that the breaker points are only required to supply base current to the transistor 22. This is only a small fraction of the current previously switched and further is supplied to an essentially resistive load. Point life is increased to such a degree that mechanical wear now actually determines point life.

While the aforenoted circuit has many advantages over standard ignition systems it is subject to two basic disadvantages, first in the response time for developing the feed-back voltage in the winding 42 of the transformer 17; and second in that high power transients are applied to the transistor during turnoff. These problems are a direct result of the response time of the system. FIGURE 2 is a modification of the aforenoted system in which the response time is decreased to increase the speed of turnoff of the transistor with an increase in ignition voltage and reduction of transients on the transistor.

In FIGURE 2 an ignition system is indicated generally by the numeral 50. A source of power, for purposes of illustration is indicated as a battery 11, one terminal of which is connected by conductor 12 to ground. The other terminal of the battery 11 is connected by conductor 13 to one side of switch 14. The other side of switch 14 is connected by conductor 15 to one side of a winding 16 of transformer 17. A resistor 18 may be inserted in the conductor 15.

The other side of the winding 16 is connected by condoctor 20 to one side of a winding 51 of a transformer 52. The other side of the winding 51 is connected by conductor 53 to emitter 21 of a transistor 22. The transistor 22 also has a collector 23 and base 24. The collector 23 is connected by conductor 25 to ground and the base 24 is connected by conductor 26 to a contact 27 of a switch 28. The switch 28 has a contact 29, adapted to mate with the contact 27, and is connected to ground by conductor 30. A zener diode 31 may be connected across the transistor 22 to protect it from high voltages by shunting voltages above the breakdown voltage of the diode around the transistor.

The transformer 17 has a secondary winding 32, one end of which is connected by conductor 33 to ground. The other side of the winding i connected by conductor 34 to the center terminal 35 of a rotary switch or distributor 36. The distributor 36 has a movable contact 37 adapted for engaging contacts 38, 38N. The contact 37 is mechanically connected to be driven by the engine (not shown). Also driven by the engine in proper sequence with the contact 37 is a cam 39 for actuating the points 28. The contacts 38, 38N are connected by respective conductors 40 to spark plugs 41,

41N. The other side of the plugs 41, 41N are connected to ground. Only One of the plugs 41 have been illustrated but it is understood that it may be a plurality thereof.

The transformer 52 has windings 54 and 55 coupled to the winding 51 by a fast response magnetic core 56. One end of the winding 54 is connected by conductor 57 and resistor 58 to one terminal of the switch 14. The other end of the winding 54 is connected by conductor 59 to the base 24 of the transistor 22. One end of the winding 55 is connected by a resistor 60 to the base 24 of the transistor 22 and the other end of the winding 55 is connected by conductor 61 to the emitter 21 of the transistor 22. A capacitor 62 may be connected across the transistor 22.

FIGURES 3 and 4 are modifications of the aforenoted circuits. In view of the detailed explanation above, it is believed that a detailed explanation is not necessary in that the modification would be understood by one skilled in the art.

In operation, closing the switch 14 connects the system to the source of energy. Means may be provided to short out the resistor 18 in order to provide a hotter .spark for starting. 1

When the contacts 27, 29 of the switch 28, which is connected mechanically to the engine to produce the opening and closing of the contacts 27 and 29 in the proper sequence, are closed, the transistor 22 is turned on by grounding the base (or supplying on drive in the case of common emitter circuits). The; opening of th contacts 27, 29 removes the path of current flow and the low impedance path across the base-emitter junction causes the transistor 22 to go to an off condition or zero current flow. This sudden drop in current flowing through the winding 16 of the transformer 17 causes a large voltage to be developed having a magnitude of E=L(di/dt). This voltage by transformer action induces a voltage in the winding 32 which is the high voltage Winding of the transformer 17 and is connected to the distributor which in turn connects to the proper spark plug. While the foregoing will generate a high voltage in the winding 32, the addition of the fast response transformer 52 substantially improves the action. The transformer 52 is normally biased at B (see FIGURE 5). In other words the NI of the winding 54 is negative. Upon the switch or points 28 being closed, the transistor 22 becomes conductive and the current through the winding 51 increases such that the NI of the winding 54 minus the N1 of the winding 51 is approximately zero. Upon the points 28 opening, the surge of current in the winding 51 is such that the transformer 52 is driven in a +3 direction with a drive equivalent to a step function of current. This drive creates a voltage in the winding 55 which is in a direction to turn off the transistor 22. The high voltage in the winding 32 of the transformer 17 is developed by the fast switching time of the transistor 22 in interrupting the current flow in the winding 51 of the transformer 52. As the current in the winding 51 drops to near zero, the voltage across the winding 55 falls to zero. The low impedance path of the winding 55 and resistor 60 causes the transistor 22 to remain off after the voltage across the winding ha fallen to zero. The transformer 52 upon the points being closed is again biased in a B direction by the winding 54 and is ready for the next cycle. Although only the common collector circuits have been described in detail, it is understood that the common emitter circuits illustrated would operate in a similar manner. In some applications, the common emitter circuit might be desirable in that the points would see a smaller voltage than in the common collector circuits.

Although several embodiments have been illustrated and described, various changes in the form and relative arrangement of the parts, which will now appear to those skilled in the art, may be made without departing from the scope of the invention.

What is claimed is:

1. An ignition system for an internal combustion engine comprising a transistor, a control transformer, a high voltage transformer, said control transformer having a bias winding, a load winding and a control winding, circuit means connecting said high voltage transformer and said load winding in series with said transistor, breaker points for energizing said bias winding to cause said transistor to conduct, and means including said control winding for biasing said transistor to a nonconducting state upon said breaker points being opened whereby the sudden collapse of current flowing in said load winding induces a high voltage in said high voltage transformer.

2. The combination as set forth in claim 1 in which a zener diode is connected across said transistor.

3. The combination as set forth in claim 1 in which a capacitor is connected between the emitter and collector of said transistor.

4. An ignition system for an internal combustion engine having a plurality of spark plugs comprising a step-up transformer having a primary and a secondary winding, a control transformer having a load winding and a control winding, a transistor, circuit means connecting said transistor in series with said primary winding and said load winding, means including a switch when in a closed position for biasing said transistor to conduct and cause current to flow in said load winding, means including said control winding to turn otI said transistor upon said switch being opened causing the current to References Cited by the Examiner collapse in said load winding and thereby induce a high UNITED STATES PATENTS voltage in said step-up transformer, and means including a distributor for connecting said secondary winding in a predetermined sequence with said switch to said spark 5 2 984 766 5/61 Moore Plugs- 3 016 476 1 62 t 5. The combination as set forth in claim 4 in which 3016477 4 igsgizg said control transformer has a fast response time. 3046447 7 /62 Kirk 6. The combination as set forth in claim 4 in which a zener diode is connected between the emitter and col- 10 GEORGE WESTBY Pnmary Exammer' lector of said transistor. RALPH G. NILSON, Examiner.

2,878,298 3/59 Giacoletto. 2,968,296 1/61 Kaehm'. 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSITON ENGINE COMPRISING A TRANSISTOR, A CONTROL TRANSFORMER, A HIGH VOLTAGE TRANSFORMER, SAID CONTROL TRANSFORMER HAVING A BIAS WINIDNG, A LOAD WINDING AND A CONTROL WINDING, CIRCUIT MEANS CONNECTING SAID HIGH VOLTAGE TRANSFORMER AND SAID LOAD WINDING IN SERIES WITH SAID TRANSISTOR, BREAKER POINTS TO ENERGIZING SAID BIAS WINDING TO CAUSE SAID TRANSISTOR TO CONDUCT, AND MEANS INCLUDING SAID CONTROL WINDING FOR BIASING SAID TRANSISTOR TO A NONCONDUCTING STATE UPON SAID BREAKER POINTS BEING OPENED WHEREBY THE SUDDEN COLLAPSE OF CURRENT FLOWING IN SAID LOAD WINDING INDUCES A HIGH VOLTAGE IN SAID HIGH VOLTAGE TRANSFORMER. 